Adequate health literacy is associated with adherence to continuous positive airway pressure in adults with obstructive sleep apnea
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Sleep Advances, 2021, 1–7
https://doi.org/10.1093/sleepadvances/zpab013
Advance Access Publication Date: 1 September 2021
Original Article
Original Article
Downloaded from https://academic.oup.com/sleepadvances/article/2/1/zpab013/6360987 by guest on 07 December 2021
Adequate health literacy is associated with
adherence to continuous positive airway pressure in
adults with obstructive sleep apnea
Claire M. Ellender1,2,*, , Sebastian Le Feuvre1, Mary Boyde3,4, Brett Duce,1,5,
Sara Winter6 and Craig A. Hukins1,2
1
Department of Respiratory & Sleep Medicine, Princess Alexandra Hospital, Brisbane, Australia, 2Faculty of
Medicine, University of Queensland, Brisbane, Australia, 3Department of Cardiology, Princess Alexandra
Hospital, Brisbane, Australia, 4School of Nursing, Midwifery and Social Work, University of Queensland,
Brisbane, Australia, 5Institute for Health and Biomedical Innovation, Queensland University of Technology,
Brisbane, Australia and 6Department of Psychology, The Prince Charles Hospital, Brisbane, Australia
*Corresponding author: Claire M. Ellender, Department of Respiratory & Sleep Medicine, Princess Alexandra Hospital, 199 Ipswich Road, Woolloongabba,
Brisbane, QLD 4102, Australia. Email: Claire.ellender@health.qld.gov.au.
Abstract
Study Objectives: Obstructive sleep apnea (OSA) is a chronic disease with significant health implications and adequate
adherence to continuous positive airway pressure (CPAP) is essential for effective treatment. In many chronic diseases,
health literacy has been found to predict treatment adherence and outcomes. In this study, the aim was to determine the
health literacy of a sleep clinic population and evaluate the association between health literacy and CPAP adherence.
Methods: A prospective cohort study was undertaken, recruiting 104 consecutive patients with a variety of sleep diagnoses.
The Short Form Rapid Estimate of Adult Literacy in Medicine (REALM-SF), a validated questionnaire, was administered to
measure health literacy. In a sub-group of 91 patients prescribed CPAP for OSA, CPAP usage was measured, with adequate
usage defined as greater than 4 h/night CPAP therapy.
Statement of Significance
Health literacy is a measurable factor that is defined as “The cognitive and social skills which determine the motivation
and ability of individuals to gain access to, understand and use information in ways which promote and maintain health”
(Nutbeam D. Defining, measuring and improving health literacy. Health Eval Promot. 2015;42:450–456). To date, only two
studies have evaluated the relationship between health literacy and continuous positive airway pressure (CPAP) adher-
ence, despite a large body of evidence in other chronic diseases linking low health literacy to worse treatment adherence
and disease outcomes. This study showed that low health literacy is associated with a twofold increased risk for inad-
equate CPAP usage. Health literacy may be an under-recognized and potentially modifiable factor for patients with OSA
who require treatment with CPAP.
Submitted: 12 July, 2021; Revised: 5 August, 2021
© The Author(s) 2021. Published by Oxford University Press on behalf of Sleep Research Society.
This is an Open Access article distributed under the terms of the Creative Commons Attribution-
NonCommercial-NoDerivs licence (https://creativecommons.org/licenses/by-nc-nd/4.0/), which permits
non-commercial reproduction and distribution of the work, in any medium, provided the original work is not
altered or transformed in any way, and that the work is properly cited. For commercial re-use, please contact 1
journals.permissions@oup.com2 | SLEEPO, 2021, Vol. 2, No. 1
Results: Seventy-one percent of the sleep clinic cohort was found to have adequate health literacy, as measured by the
REALM-SF. In those prescribed CPAP for OSA, inadequate health literacy was associated with a twofold increased risk for
inadequate CPAP usage (adjusted odds ratio [OR] 2.9, 95% CI: 1.1 to 8.22, p = 0.045). There was a 1.7 h/night difference in
median CPAP usage comparing those with adequate to inadequate health literacy (4.6 h vs. 6.3 h/night).
Conclusions: The majority of this sleep disorders cohort had adequate health literacy as measured by the REALM-SF
questionnaire. However, inadequate health literacy appears to be an independent predictor of treatment adherence and
may represent a modifiable risk factor of poor treatment outcomes in OSA.
Key words: CPAP usage; CPAP adherence; CPAP compliance; health literacy; obstructive sleep apnea
Background secondary outcome; one found a nonsignificant trend toward
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Obstructive sleep apnea (OSA) is a prevalent sleep disorder asso- poor adherence with low health literacy, and the other found
ciated with significant health and financial implications [1, 2]. The no significant relationship [8, 17]. The present study aimed to
treatment of choice for the majority of symptomatic OSA patients measure health literacy in a cohort of incident and prevalent pa-
is continuous positive airway pressure (CPAP) [3]. The minimum tients treated in a tertiary hospital sleep clinic. We hypothesized
duration of CPAP per night to achieve symptomatic improvements that the proportion of patients with adequate health literacy in
in day time sleepiness [4] and neurocognitive performance [5] is a sleep clinic population would be lower than the 75% previously
4 h per night; however, in severe OSA, CPAP duration over 6.5 h per described nonclinical population. A secondary aim of this study
night is required to normalize obstructive events [6]. Adherence was to evaluate the association between health literacy and
to CPAP therapy of more than 4 h a night remains low (ranging CPAP adherence, independent of SES.
from 40% to 60% [7]). Of the patient demographic factors that pre-
dict adequate CPAP adherence, socioeconomic deprivation has
been shown to predict poor usage [8]. In other chronic disease, METHODS
socio-economic status (SES) and treatment adherence have been
Study participants
linked through the concept of health literacy [9].
The World Health Organization defines health literacy as Following approval of Metro South Human Research and Ethics
“The cognitive and social skills which determine the motivation Committee (HREC 2018/QPAH/98), participants were recruited
and ability of individuals to gain access to, understand and from a public sleep disorders outpatient clinic in Brisbane,
use information in ways which promote and maintain health” Australia over a 4-month period, 2018–2019. Inclusion criteria
[10]. In the USA it is estimated that only a third of adults have included age ≥18 years, no past medical history consistent
basic health literacy [11] and similarly only approximately 40% with cognitive impairment and any sleep diagnosis was per-
of adult Australians have adequate health literacy sufficient to mitted. All incident and prevalent patients of the service
comprehend patient educational material [12]. Low individual were approached to participate. Exclusion criteria were age
health literacy is associated with higher rates of hospitalization less than 18 years, those unable to provide informed consent
and emergency care, as well as higher rates of adverse outcomes and inability to read or write in English. Demographic data,
generally [13]. Several validated tools for assessing health lit- anthropomorphic, years of education, socioeconomic decile
eracy exist in the literature. Two commonly utilized question- (index of relative socio-economic advantage and disadvan-
naires are the Short Test of Functional Health Literacy in Adults tage, index of economic resources (IER) and index of edu-
(takes 10 min to administer) and the Short Form Rapid Estimate cation and occupation (IEO) [18]) were recorded. The three
of Adult Literacy in Medicine (REALM-SF; takes 3 min to ad- measures of SES recorded, capture varied aspects of relative
minister) and have been validated across a variety of patient advantage and/or disadvantage from post code census data.
populations [14]. These tools are not disease specific, but rather The “index of relative socio-economic advantage and disad-
correlated with literacy, numeracy and compression skills and vantage” (IRSAD) is a composite calculated from a locations
thresholds below which individuals have difficulty with health proportion of residents with low-income, labor intensive jobs,
educational material. disability or chronic disease, one parent families, rent under
Few attempts have been made to utilize these tools to assess $AUD215 per week and unemployed status [18]. Lower IRSAD
the level of health literacy amongst the OSA population, or to decile indicates greater disadvantage and lack of advantage.
evaluate whether poor health literacy is a risk factor for OSA IER incorporates financial measures of SES and is calculated
and/or a predictor of treatment adherence. Li et al. [15] evalu- as a composite of factors such as proportion of high versus
ated men aged over 40 years in an Australian chronic disease low-income households and rent versus home ownership [18].
screening cohort, and found adequate health literacy amongst IEO reflects educational level of a local community and occu-
75.3% of previously diagnosed and 68% previously undiagnosed pational advantage [18].
OSA. The authors do note, however, that the cohort was better The CONSORT statement of patient recruitment is shown
educated and reported better health than the general popula- in Figure 1, indicating the number of “eligible and recruited,”
tion. Thus, the results may not be representative of a general “potentially eligible but not assessed,” “ineligible,” and pa-
sleep clinic population. Adherence to therapy in other chronic tients whom specifically “declined recruitment,” as there were
diseases such as HIV, asthma, and diabetes has been strongly a number of patients eligible but not screened due to clinical
linked to an individual’s level of health literacy [16]. The rela- workload.
tionship between CPAP adherence and health literacy has been OSA was defined as per American Association of Sleep
evaluated in only two trials, in which health literacy was a Medicine testing criteria [19] and all other sleep diagnosisEllender et al. | 3
according to Sleep Physician assessment using the ICSD-3 def- RESULTS
initions [20].
Two hundred and one patients met the eligibility criteria and full
a complete data set was available for 104 participants. Ninety-
one of these patients were recommended for CPAP therapy.
Health literacy assessment
Demographics of the cohort are shown in Table 1. The cohort
Health literacy was assessed using the REALM-SF, which in- had an almost equal proportion of men and women who pre-
volves the patient reading and pronouncing seven English dominantly had severe OSA; only three had no sleep disorder
medical words arranged in ascending order of difficulty. Points breathing. Comparisons were made between eligible patients
are given for correctly pronounced words within a 3-minute who were and were not enrolled, as shown in Supplement Table
timeframe. Correct responses of 4–6 words correspond to a S1. There were no significant differences between these groups
seventh to eighth grade reading level, 1–3 words correspond to according to age, sex, education levels, or socioeconomic factors.
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fourth to sixth grade level, and a score of 0 indicates literacy There was, however, a trend towards more university-educated
of third grade and below [5]. Inadequate health literacy was de- patients in the sampled population compared with un-sampled.
fined as an REALM-SF score less than or equal to 6 [21]. The pri-
mary endpoint of the study was the proportion of patients with
REALM-SF > 6. Staff administering the REALM-SF assessment Health literacy
were blinded to the sleep and socioeconomic outcomes of the
Health literacy as measured by REALM-SF was found to be ad-
patients they were assessing. Clinicians treating the sleep dis-
equate in 71 (71%) of patients. Higher REALM-SF health literacy
orders were blinded to the REALM-SF outcome.
was associated with increased years of education (β 0.36, 95% CI:
0.11 to 0.61, p = 0.05) and higher SES postcode-decile (β 0.49, 95%
CI: 0.15 to 0.83, p = 0.005). In this cohort, adequate health literacy
CPAP adherence in OSA subgroup
was more common in women (p = 0.05), shown in Table 2. There
In patients with OSA on CPAP, a prespecified subgroup analysis was no significant difference in adequate health literacy be-
was planned to evaluate therapy usage as a secondary outcome tween incident (74%) and prevalence (67%) CPAP users, p = 0.49.
measure. Objective CPAP usage was downloaded from the CPAP
device and recorded as mean hours of usage per day. For incident
patients, CPAP usage was determined at the next clinic follow CPAP adherence
up, which was at the 2-month post REALM-SF assessment visit.
Patients with inadequate health literacy had significantly re-
For prevalent CPAP patients, usage was obtained from download
duced CPAP usage (4.6 h per night, IQR 0.4–7.0), compared to pa-
of the machine on the same day health literacy assessment.
tients with adequate health literacy (6.3 h per night, IQR 4.3–7.6)
All patients commencing CPAP therapy had in-laboratory edu-
p = 0.02, shown in Figure 2 and Table 3; unadjusted OR 3.03 (95%
cation from sleep scientific staff at the time of CPAP titration
study. This includes a standard two-page educational brochure
that explains the rational for CPAP therapy and troubleshooting.
Adequate CPAP usage was defined as ≥4 h/night adequate usage,
and4 | SLEEPO, 2021, Vol. 2, No. 1
CI: 1.17 to 7.8, p = 0.03). Overall, CPAP usage was 6 h per night by three SES measures were not associated with differences in
(IQR 3.22–7.37), with 75/91 (82%) of those patients prescribed CPAP usage in this cohort. This is contrasting from findings by
CPAP therapy, taking up the treatment. Women did have signifi- Bakker et al. [8] in which SES was significantly associated with
cantly higher median CPAP usage 6.5 h (IQR 5.21–7.5) compared CPAP adherence and 20% of the variance of CPAP adherence was
with men 4.46 h (IQR 0.62–6.9) p = 0.01 (see Supplementary Table found to be due to low SES and lower education. Possible ex-
S2 for more details). Women did not have significantly higher planation for this difference may be the Bakker et al. [8] cohort
education, socioeconomic decile and were of similar age to the drew from a high proportion First Nations Māori population with
men prescribed CPAP; however, the women in this cohort had a unique sociocultural environments.
trend toward worse symptoms (Epworth Sleepiness Scale 10 for Psychological factors are more consistently predictive of
women and 8 for men p = 0.05). Incident users of CPAP had lower CPAP adherence in the literature—those individuals with high
adherence compared with prevalent users (median CPAP usage perceived functional limitation from OSA sleepiness and high
4.4 h IQR 3.1–5.34 vs. 6.3 h IQR 4.9–6.6, p = 0.039). There was a self-efficacy to problem solve side effects are likely to adhere to
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nonsignificant trend toward improved CPAP uptake in those with CPAP [26]. Health literacy and self-efficacy appear to be intercon-
adequate health literacy (57/64 or 89% patients with adequate nected; health literacy is likely to facilitate the motivation and
health literacy commenced CPAP and 20/27 or 74% with inad- capacity within the individual to obtain health information, and
equate commenced CPAP p = 0.07). self-efficacy is likely to facilitate the ability to organize and im-
Adjusting for sex, incident/prevalence, and Epworth plement health-promoting activities. Health literacy is thought
Sleepiness Scale, inadequate health literacy was still signifi- to be the mediator between disadvantage and poor health out-
cantly associated with a twofold increased risk for inadequate comes in other chronic disease such as diabetes, however, rep-
CPAP usage (OR 2.9, 95% CI: 1.1 to 8.22, p = 0.04). CPAP adherence resents a potentially modifiable risk factor [27]. Health literacy in
was not significantly associated with age, Epworth Sleepiness the current study was higher in women compared to men, this
Scale, Respiratory Disturbance Index, years of education, or is in keeping with previous national data in this age range [28].
socioeconomic decile (see Supplementary Table S3 for further Obtaining a diagnosis of OSA starts with navigating diag-
details). Female sex was neither a significant mediator (a1 = 0.19, nostic testing which may exclude low health literacy patients,
b1 = 0.35, c′ = 1.67, 95% CI: −0.14 to 0.47), nor moderator (p = 0.42) due to the complexity of study requirements, particularly in
of the relationship between health literacy and CPAP adherence. home-based programs. Then, navigating the common complica-
tions of CPAP such as mask fit, nasal congestion, aerophagia and
Discussion Table 1. Patient demographics
In this study, health literacy was measured with the REALM-SF N (%)
questionnaire in a sleep clinic population at a tertiary public
Number 104
hospital and 71% were found to have adequate health literacy.
Males, n (%) 50 (48%)
Of those 91 patients prescribed CPAP therapy, adherence to CPAP Age, years 59 ±14
was 1.7 h per night greater in those with adequate health lit- Body mass index, kg/m2 38 (32–44)
eracy, compared to those with inadequate health literacy. This Years of education, n (%)
study has found that inadequate health literacy puts patients Grade 10 or below 38 (36.5%)
with OSA at a more than twofold risk of inadequate CPAP usage. Grade 12 7 (6.7%)
The data surrounding CPAP adherence and baseline disease Certificate/apprenticeship 40 (38.5%)
and patient demographics in the literature are inconsistent. University 19 (18.3%)
SES decile by postcode 5 (3–8)
Comparable with other series, CPAP adherence in this co-
SES decile by resource 5 (3–8)
hort was not associated with Apnea Hypopnea Index, Epworth
SES decile by occupation 4 (2–7)
Sleepiness Scale, socioeconomic factors, nor years of education.
Country of birth, n (%)
Sex was a significant influence on our cohort on adherence, with Australia 85 (81%)
females 3.5 times more likely to have CPAP usage > 4 h per night New Zealand 7 (7%)
than men. This difference in CPAP usage in this cohort aberrant UK 4 (4%)
compared to many other series [22, 23] and is not explained by Other 8 (8%)
common confounders (age, SES, years of education), however Epworth Sleepiness Scale 8 (4–13)
may be explained by higher Epworth Sleepiness Scale in the fe- RDI, events/hour 27 (16-60)
males of this cohort, compared with men. Epworth Sleepiness Sleep diagnosis, n (%)
Mild OSA 21 (20%)
Scale consistently is a predictor for adherence, with baseline
Moderate OSA 28 (27%)
severe symptoms and large improvements in sleepiness in the
Severe OSA 49 (47%)
first months predicting long term response [22]. In our cohort,
Other/ no sleep disorder 6 (6%)
there was a large variance in Epworth Sleepiness Scale and in- CPAP usage hours 6.0 (3.2–7.4)
adequate sample size is the likely explanation for this difference CPAP usage > 4 h, n (%) 63 (61%)
compared with larger previously published series. This cohort REALM-SF > 6, n (%) 74 (71.2%)
had high CPAP long-term usage compared with many other pub-
lished series; however the data are in keeping with the 10-year Data are presented as number (percent), mean ± standard deviation or median
(interquartile range) where appropriate.
average CPAP usage from the clinic [24, 25]. The in-laboratory
SES, socio-economic status; RDI, respiratory disturbance index; UK, United
CPAP educational and on-call troubleshooting program may Kingdom; OSA, obstructive sleep apnea; CPAP, continuous positive airway pres-
be an explanation for this. Socioeconomic factors as measured sure; REALM-SF, Short Form Rapid Estimate of Adult Literacy in Medicine.Ellender et al. | 5
dry mouth [29] often require problem-solving skills with written The test-retest reliability coefficient is 0.99, an interrater re-
information in complex device manuals. Furthermore, the ma- liability of 0.99 and high construct validity, with strong cor-
jority of sleep unit informational hand-outs are in written form, relations with other measures of literacy [33]. It has been
which is potentially problematic for individuals with low lit- validated in populations similar to the demographics seen
eracy. The higher rates of adequate health literacy seen in this in the current study, and is faster to administer than alter-
study and Li et al. [15] compared with other chronic disease may natives such as TOFHLA [33]. However, the weaknesses of
reflect referral bias, as barriers to sleep disorders services may this measure include potential racial bias, no assessment of
exclude low health literacy patients from being represented in numerical literacy, it is not specific for sleep disorders know-
these sampled populations [15]. It is of concern that nearly 30% ledge, nor does it test comprehension [33]. The REALM-SF is
of patients were assessed as having low health literacy, which is not a based on a conceptual framework of health literacy and
likely to limit their ability to successfully implement and adhere was developed from literacy measures. Other weaknesses of
to recommended OSA treatment. the current study include the lack of inclusion of 94 patients,
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Behavioral interventions have the strongest evidence in who were not assessed but would have been eligible. The gap
improving CPAP adherence [30]. However, these interventions analysis performed is at least reassuring, as there were no sig-
are labor intensive, with the majority of the interventions re- nificant demographic differences between the sampled and
viewed in a recent Cochrane review requiring greater than 2 h unsampled-eligible populations. The study is not randomized,
of clinician time. Educational interventions to improve CPAP ad- however, there was blinding of health literacy assessors from
herence have been shown to improve CPAP adherence, with a those assessing CPAP adherences. While common confounders
mean difference of +0.85 h, however, the quality of evidence is such as disease severity, SES, and age were considered, marital
low [30], with a number of the studies demonstrating equivocal status and ethnicity were not and those with self-identified
results with wide confidence intervals. None of the educational insufficient English language skills were excluded. Three pa-
studies have been specifically designed for patients with inad- tients out of 107 were not included in the analysis due to
equate health literacy, which may be a factor in the equivocal missing data, which is a potential weakness of the analysis.
outcomes. This study points to health literacy as a factor that Given the findings of this study, clinicians and sleep services
needs consideration when developing educational approaches should consider health literacy as a flag for vulnerable individuals
to enhance CPAP adherence; clinicians need to incorporate com-
munication strategies specifically designed to address the needs
of individuals with low health literacy. From other chronic dis-
ease literature, there is evidence that screening for low health
literacy, alters clinician’s communication style, and increases
the likelihood of using pictures, diagrams, and involving family
members [31]. Plain language initiative encourages communica-
tors to know the literacy level of their audience, screen for base-
line knowledge and increase the use of visuals and videos [32].
Strengths of this study include the prospective design, and
the blinding of health literacy assessors and clinicians. The
REALM-SF is a well-validated and quick-to-administer meas-
urement of health literacy, taking under 3 min to administer.
Figure 2. Unadjusted CPAP usage (hours) by health literacy status.
Table 2. Demographics according to level of health literacy (N = 104)
REALM-SF > 6 REALM-SF ≤ 6 P
Table 3. Health literacy and CPAP outcomes (N = 91)
Number 74 (71%) 30 (29%)
Male 31 19 0.05* REALM-SF > 6 REALM-SF ≤ 6 P
Female 43 11
Age, years 59±13 57±16 0.55 Number 64 (70%) 27 (30%)
Body mass index, kg/m2 38 (33–44) 39 (30–44) 0.98 Male 26 16 0.11
Years of education Female 38 11
Grade 10 or below 25 13 0.03* Age, years 60±12 57±17 0.33
Grade 12 3 4 Body Mass Index, kg/m2 38 (33.75–45) 39 (32–47) 0.95
Certificate/apprenticeship 28 12 Epworth sleepiness scale 8.5 (4–14) 8 (7–12) 0.78
University 18 1 RDI, events/hour 30 (17–69) 40 (19–59) 0.68
Epworth sleepiness scale 8 (4–14) 9 (6.7–12) 0.95 CPAP usage hours 6.3 (4.3–7.6) 4.6 (0.4–7.0) 0.02*
RDI, events/hour 27 (14–61) 37 (15–57) 0.82 CPAP usage ≥ 4 h/night 49 14 0.04*
SES decile by postcode 6 (3–8) 3 (2–7) 0.02* SES decile by postcode 6 (3–8) 3 (2-6) 0.1
SES decile by resource 5.5 (3.75–8) 4 (3–7.25) 0.13 SES decile by resource 6 (4–8) 3 (3-7) 0.13
SES decile by occupation decile 5 (2–7.25) 2 (1–4) 0.01* SES decile by occupation 5 (2–7) 2 (1.5-4) 0.01*
Data are presented as number, mean ± standard deviation or median (inter- Data are presented as either number, mean ± standard deviation or median
quartile range) where appropriate. (interquartile range) where appropriate.
RDI, respiratory disturbance index; SES, socio-economic status; REALM-SF, RDI, respiratory disturbance index; SES, socio-economic status; REALM-SF,
Short Form Rapid Estimate of Adult Literacy in Medicine. Short Form Rapid Estimate of Adult Literacy in Medicine.
*P < 0.05. *P < 0.05.6 | SLEEPO, 2021, Vol. 2, No. 1
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Financial Disclosure Statement
tors and comorbidities in a population cohort of men. Sleep.
None to declare.
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Nonfinancial Disclosure Statement
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Conflict of Interest: The authors declare no competing
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